Trunk (thorax, abdomen, back)

Diaphragm

Diaphragma

Origin

Xiphoid process, inner surface of the lower six ribs/costal cartilage, and via the crura from the lumbar vertebrae (L1-L3)

Insertion

Central tendon, the central tendinous sheet of the diaphragm

Function

Primary muscle of respiration: contraction flattens the dome and increases thoracic volume (inspiration)

Innervation

Phrenic nerve (C3-C5)

Movement & chain

Works almost in isolation during quiet breathing; during exertion in synergy with the external intercostals and accessory respiratory muscles. Also plays a role in abdominal straining (Valsalva) together with the abdominal muscles.

Palpation

Not directly palpable; its movement can be observed indirectly via expansion of the lower ribs and abdominal wall during deep inspiration.

Clinical

Elevation or paresis (e.g. with phrenic nerve injury after neck or thoracic surgery) causes shortness of breath and paradoxical abdominal movement. Hiatal hernias arise from weakening of the esophageal opening.

Segmental innervation

Phrenic nerve, myotome C3-C5 ("C3, 4, 5 keep the diaphragm alive").

In clinical practice

Relevant landmark in ventilation and pulmonary function testing; elevation on X-ray/CT can indicate phrenic nerve palsy or atelectasis.

Region in the model

Trunk (thorax, abdomen, back)